Brief Description of the Prior Art
Compositions comprising EVOH and drying agents are disclosed in U.S. Pat. Nos. 4,425,410 and 4,464,443, indicating that multi-layer structures foregoing comprising the compositions exhibit a small increase in oxygen permeability even after a retort (steam sterilization) treatment, as compared to when EVOH alone is used and are, therefore, preferable as packaging materials.
When a container is prepared in accordance with the method disclosed in the foregoing U.S. patents and employed for food storage, which requires a retort, gas permeability resistance is improved as compared to the case of using EVOH alone but the degree of the improvement is still insufficient and the container is unsatisfactory for purposes of improving storability of food which requires a steam sterilization treatment to a high degree. On the other hand, as a method for preventing increase in the rate of oxygen permeability upon retort treatment of multi-layer structures comprising EVOH, there are known methods which comprises blending a drying agent in an adhesive resin layer, etc. proximate to EVOH, as shown in U.S. Pat. No. 4,407,897 or Published Unexamined Japanese Patent Application No. 170748/82. In these cases, the adhesive resin layer containing the drying agent should be used in a thick thickness in order to obtain effective results. Such causes a problem from an economical viewpoint and in addition, the effects are not satisfactory from a practical standpoint (Comparative Example 4).
Under such circumstances, the present inventors have made extensive investigations on molding techniques over a wide range for purposes of controlling the blended state of a blend composition and studied the relationship between the blended state of the obtained composition and the rate of oxygen permeability of multi-layer structures therefrom upon a retort treatment. As a result, it has been found that the graininess and the dispersion state of the drying agent grains in an EVOH matrix greatly affect the rate of oxygen permeability. A composition free from the defects as described above was thereby obtained.